Effect of peat quality on microbial greenhouse gas formation in an acidic fen

Peatlands play an important role in the global carbon cycle and represent both an important stock of soil carbon and a substantial natural source of relevant greenhouse gases like CO₂ and CH₄. While it is known that the quality of organic matter affects microbial degradation and mineralization processes in peatlands, the manner in which the quality of peat organic matter affects the formation of CO₂ and CH₄ remains unclear. In this study we developed a fast and simple peat quality index in order to estimate its potential greenhouse gas formation by linking the thermo-degradability of peat with potential anaerobic CO₂ and CH₄ formation rates. Peat samples were obtained at several depths (0–40 cm) at four sampling locations from an acidic fen (pH 4.7). CO₂ and CH₄ formation rates were highly spatially variable and depended on depth, sampling location, and the composition of pyrolysable organic matter. Peat samples active in CO₂ and CH₄ formation had a quality index above 1.35, and the fraction of thermally labile pyrolyzable organic matter (comparable to easily available carbon substrates for microbial activity) obtained by thermogravimetry was above 35%. Curie-point pyrolysis-gas chromatography/mass spectrometry mainly identified carbohydrates and lignin as pyrolysis products in these samples, indicating that undecomposed organic matter was found in this fraction. In contrast, lipids and unspecific pyrolysis products, which indicate recalcitrant and highly decomposed organic matter, correlated significantly with lower CO₂ formation and reduced methanogenesis. Our results suggest that undecomposed organic matter is a prerequisite for CH₄ and CO₂ development in acidic fens. Furthermore, the new peat quality index should aide the estimation of potential greenhouse gas formation resulting from peatland restoration and permafrost thawing and help yield more robust models of trace gas fluxes from peatlands for climate change research

Revisiting Mt. Kilimanjaro : Do n-alkane biomarkers in soils reflect the δ2H isotopic composition of precipitation?

Abstract. During the last decade compound-specific deuterium (δ2H) analysis of plant leaf wax-derived n-alkanes has become a promising and popular tool in paleoclimate research. This is based on the widely accepted assumption that n-alkanes in soils and sediments generally reflect δ2H of precipitation (δ2Hprec). Recently, several authors suggested that δ2H of n-alkanes (δ2H,sub&gt;n-alkanes) can also be used as proxy in paleoaltimetry studies. Here we present results from a δ2H transect study (~1500 to 4000 m a.s.l.) carried out on precipitation and soil samples taken from the humid southern slopes of Mt. Kilimanjaro. Contrary to earlier suggestions, a distinct altitude effect in δ2Hprec is present above ~2000 m a.s.l., i.e. δ2Hprec values become more negative with increasing altitude. The compound-specific δ2H values of nC27 and nC29 do not confirm this altitudinal trend, but rather become more positive both in the O-layers (organic layers) and the Ah-horizons (mineral topsoils). Although our δ2Hn-alkane results are in agreement with previously published results from the southern slopes of Mt. Kilimanjaro (Peterse et al., 2009, BG, 6, 2799–2807), a major re-interpretation is required given that the δ2Hn-alkane results do not reflect the δ2Hprec results. The theoretical framework for this re-interpretation is based on the evaporative isotopic enrichment of leaf water associated with transpiration process. Modelling results show that relative humidity, decreasing considerably along the southern slopes of Mt. Kilimanjaro (from 78% at ~ 2000 m a.s.l. to 51% at 4000 m a.s.l.), strongly controls δ2Hleaf water. The modelled δ2H leaf water enrichment along the altitudinal transect matches well the measured 2H leaf water enrichment as assessed by using the δ2Hprec and δ2Hn-alkane results and biosynthetic fractionation during n-alkane biosynthesis in leaves. Given that our results clearly demonstrate that n-alkanes in soils do not simply reflect δ2Hprec but rather δ2Hleaf water, we conclude that care has to be taken not to over-interpret δ2Hn-alkane records from soils and sediments when reconstructing δ2H of paleoprecipitation. Both in paleoaltimetry and in paleoclimate studies changes in relative humidity and consequently in δ2Hn-alkane values can completely mask altitudinally or climatically-controlled changes in δ2Hprec. </jats:p

Reconstruction of the Late Holocene climate and environmental history from North Bolgoda Lake, Sri Lanka, using lipid biomarkers and pollen records

The catastrophic impact and unpredictability of the Indian Ocean Monsoon (IOM) over South Asia are evident from devastating floods, mudslides and droughts in one of the most densely populated regions of the globe. However, our understanding as to how the IOM has varied in the past, as well as its impact on local environments, remains limited. This is particularly the case for Sri Lanka, where erosional landscapes have limited the availability of well-stratified, high-resolution terrestrial archives. Here, we present novel data from an undisturbed sediment core retrieved from the coastal Bolgoda Lake. This includes the presentation of a revised Late Holocene age model as well as an innovative combination of pollen, source-specific biomarkers, and compound-specific stable carbon isotopes of n-alkanes to reconstruct the shifts in precipitation, salinity and vegetation cover. Our record documents variable climate between 3000 years and the present, with arid conditions c. 2334 and 2067 cal a bp. This extreme dry period was preceded and followed by more wet conditions. The high-resolution palaeoenvironmental reconstruction fills a major gap in our knowledge on the ramifications of IOM shifts across South Asia and provides insights during a time of major redistribution of dense human settlements across Sri Lanka.Introduction Background, materials and methods - Study area and site - Sampling - Age–depth model - Biomarker analysis - Compound‐specific carbon isotope analysis - Pollen analysis Results - Chronology and climate zones - Biomarker trends and ratios of n‐alkanes - Triterpenols - δ13C isotopes in n‐alkanes - Pollen Discussion - Palaeoenvironmental implications - Mangrove vegetation, palaeosalinity changes and droughts - Palaeoclimate and palaeoenvironmental reconstruction - Zone 1 (2960 to 2390 cal a bp; 385–252 cm) - Zone 2 (2390 to 1800 cal a bp; 252–140 cm) - Zone 3 (1800 to 1318 cal a bp; 140–60 cm) - Zone 4 (1318 cal a bp to present; 60–0 cm) - South Asian comparisons and potential human implications Conclusion

The stable isotopic signature of biologically produced molecular hydrogen (H₂)

Biologically produced molecular hydrogen (H₂) is characterised by a very strong depletion in deuterium. Although the biological source to the atmosphere is small compared to photochemical or combustion sources, it makes an important contribution to the global isotope budget of H₂. Large uncertainties exist in the quantification of the individual production and degradation processes that contribute to the atmospheric budget, and isotope measurements are a tool to distinguish the contributions from the different sources. Measurements of &delta; D from the various H₂ sources are scarce and for biologically produced H₂ only very few measurements exist. <br><br> Here the first systematic study of the isotopic composition of biologically produced H₂ is presented. In a first set of experiments, we investigated &delta; D of H₂ produced in a biogas plant, covering different treatments of biogas production. In a second set of experiments, we investigated pure cultures of several H₂ producing microorganisms such as bacteria or green algae. A Keeling plot analysis provides a robust overall source signature of &delta; D = &minus;712&permil; (±13&permil;) for the samples from the biogas reactor (at 38 °C, &delta; D_H2O= +73.4&permil;), with a fractionation constant &varepsilon;_H2-H2O of −689&permil; (±20&permil;) between H₂ and the water. The five experiments using pure culture samples from different microorganisms give a mean source signature of &delta; D = &minus;728&permil; (±28&permil;), and a fractionation constant &varepsilon;_H2-H2O of −711&permil; (±34&permil;) between H₂ and the water. The results confirm the massive deuterium depletion of biologically produced H₂ as was predicted by the calculation of the thermodynamic fractionation factors for hydrogen exchange between H₂ and water vapour. Systematic errors in the isotope scale are difficult to assess in the absence of international standards for &delta; D of H₂. <br><br> As expected for a thermodynamic equilibrium, the fractionation factor is temperature dependent, but largely independent of the substrates used and the H₂ production conditions. The equilibrium fractionation coefficient is positively correlated with temperature and we measured a rate of change of 2.3&permil; / °C between 45 °C and 60 °C, which is in general agreement with the theoretical prediction of 1.4&permil; / °C. Our best experimental estimate for &varepsilon;_H2-H2O at a temperature of 20 °C is −731&permil; (±20&permil;) for biologically produced H₂. This value is close to the predicted value of −722&permil;, and we suggest using these values in future global H₂ isotope budget calculations and models with adjusting to regional temperatures for calculating &delta; D values

Proposed Diagnostic Criteria and Classification of Canine Mast Cell Neoplasms: A Consensus Proposal

Mast cell neoplasms are one of the most frequently diagnosed malignancies in dogs. The clinical picture, course, and prognosis vary substantially among patients, depending on the anatomic site, grade and stage of the disease. The most frequently involved organ is the skin, followed by hematopoietic organs (lymph nodes, spleen, liver, and bone marrow) and mucosal sites of the oral cavity and the gastrointestinal tract. In cutaneous mast cell tumors, several grading and staging systems have been introduced. However, no comprehensive classification and no widely accepted diagnostic criteria have been proposed to date. To address these open issues and points we organized a Working Conference on canine mast cell neoplasms in Vienna in 2019. The outcomes of this meeting are summarized in this article. The proposed classification includes cutaneous mast cell tumors and their sub-variants defined by grading- and staging results, mucosal mast cell tumors, extracutaneous/extramucosal mast cell tumors without skin involvement, and mast cell leukemia (MCL). For each of these entities, diagnostic criteria are proposed. Moreover, we have refined grading and staging criteria for mast cell neoplasms in dogs based on consensus discussion. The criteria and classification proposed in this article should greatly facilitate diagnostic evaluation and prognostication in dogs with mast cell neoplasms and should thereby support management of these patients in daily practice and the conduct of clinical trials

Einfluss der Insektenherbivorie auf den Kreislauf fester und gelöster organischer Substanzen in einem Grasslandökosystem - eine Mesokosmenstudie

Insektenmassenvermehrungen können durch die Reduktion von oberirdischer Biomasse (z.B. Blattverlust) und Koteintrag Einfluss auf den Kreislauf der organischen Substanz in Ökosystemen nehmen und dadurch zeitlich und räumlich begrenzte massive Veränderungen biogeochemischer Reaktionsraten hervorrufen. Um die Auswirkungen auf den C- und N-Kreislauf in Grasländern im System Herbivore-Pflanze-Boden zu quantifizieren, wurde ein Mesokosmenexperiment (D: 50 cm, H: 100 cm) mit Knäuelgras (Dactylis glomerata) und Heuschrecken (Chorthippus dorsatus) durchgeführt. Mit Hilfe von C-13-O2-Gas und N-15 markiertem Kot (δN-15: 58‰) wurde der C- und N-Pfad in den Kompartimenten Blatt, Wurzel, Grashüpfer, Kot, Boden und in der Eintrags- und Bodenlösung verfolgt. Es wurden folgende vier Varianten durchgeführt (n=3): Kontrolle; C-13-O2; C-13-O2+20_Grashüpfer; C-13-O2+20_Grashüpfer+N-15-markierter Kot (+9.2 µg N*cm-2). Innerhalb einer 5-Tage-Inkubation wurden die Kosmen bewässert (13 mm/5d). Nach fünf Tagen wurden die Bodenlösungen und die Kaltwasser- sowie mikrobielle Biomasse-Extrakte (CFE) (0-4, 4-12 cm) auf gelösten OC, OδC-13 und N untersucht. Ebenfalls wurden TOC, δC-13, TN sowie δN-15 Werte aller Kompartimente bestimmt. Nach fünf Tagen waren sowohl die Grashüpfer, der Kot als auch die Eintragslösung des Kotes signifikant mit C-13 angereichert. C-13 wurde stärker in Wurzeln als in Blätter eingebaut (anhand δC-13-Werten). Erhöhte DOC-13 Werte im Boden weisen auf einen schnellen Blatt-C-Kreislauf über Grashüpfer, Kot bis in die Bodenlösung, die Bodenorganismen und die Graswurzeln hin. Dies wird ebenfalls durch den zugegebenen N-15 Kot deutlich, welcher um 91% seines Gesamt-N-Gehaltes reduziert wurde. Es scheint eine schnelle N-Freisetzung durch Auswaschung und Wurzelaufnahme (-0.82±0.28‰ vs -1.54±0.12‰) stattgefunden zu haben. N-15 war im frisch produzierten Kot (0.62±0.4‰ vs -0.14 ±0.27‰) aber nicht in den Blättern angereichert. Die Herbivorie hatte keinen Einfluss auf die N-Menge in der Bodenlösung und in den Extrakten, was eine schnelle Pflanzenaufnahme des freigewordenen N vermuten lässt. Die geringe N-Konzentration des Mineralbodens (0.14%) und der Bodenlösungen (1-2.3 mg*L-1) weisen im Allgemeinen auf eine geringe Pflanzen-N-Verfügbarkeit hin. Wir schließen daraus, dass innerhalb des kurzen zeitlichen Umfanges (5d) N-limitierte Weidesysteme robust auf starken Insektenbefall reagieren und nicht zu signifikanten, ökosystemaren N-Auswaschungsverlusten neigen

Microbial community functioning during plant litter decomposition

International audienceAbstract Microbial life in soil is fueled by dissolved organic matter (DOM) that leaches from the litter layer. It is well known that decomposer communities adapt to the available litter source, but it remains unclear if they functionally compete or synergistically address different litter types. Therefore, we decomposed beech, oak, pine and grass litter from two geologically distinct sites in a lab-scale decomposition experiment. We performed a correlative network analysis on the results of direct infusion HR-MS DOM analysis and cross-validated functional predictions from 16S rRNA gene amplicon sequencing and with DOM and metaproteomic analyses. Here we show that many functions are redundantly distributed within decomposer communities and that their relative expression is rapidly optimized to address litter-specific properties. However, community changes are likely forced by antagonistic mechanisms as we identified several natural antibiotics in DOM. As a consequence, the decomposer community is specializing towards the litter source and the state of decomposition (community divergence) but showing similar litter metabolomes (metabolome convergence). Our multi-omics-based results highlight that DOM not only fuels microbial life, but it additionally holds meta-metabolomic information on the functioning of ecosystems

The unexpectedly short Holocene Humid Period in Northern Arabia

The early to middle Holocene Humid Period led to a greening of today's arid Saharo-Arabian desert belt. While this phase is well defined in North Africa and the Southern Arabian Peninsula, robust evidence from Northern Arabia is lacking. Here we fill this gap with unprecedented annually to sub-decadally resolved proxy data from Tayma, the only known varved lake sediments in Northern Arabia. Based on stable isotopes, micro-facies analyses and varve and radiocarbon dating, we distinguish five phases of lake development and show that the wet phase in Northern Arabia from 8800-7900 years BP is considerably shorter than the commonly defined Holocene Humid Period (similar to 11,000-5500 years BP). Moreover, we find a two century-long peak humidity at times when a centennial-scale dry anomaly around 8200 years BP interrupted the Holocene Humid Period in adjacent regions. The short humid phase possibly favoured Neolithic migrations into Northern Arabia representing a strong human response to environmental changes